Radiotherapy treatment using medical axis transformation

Abstract

The medial axis analysis of an object can be used to effectively guide and optimize radiosurgery treatment planning. In this method, a fast Euclidean medial axis transformation in three dimensions based on dynamic grassfire simulation and ridge extraction is presented. A ridge occurs when fire fronts collapse during grassfire propagation. Iso-contours(2D) or iso-surfaces(3D) can be obtained from dynamic grassfire transforms. They are locally smooth everywhere except at ridge locations. Ridges are detected by measuring local curvature at each point. This process is invariant under spatial translations and rotations. In radiosurgery treatment planning, optimal shots are only placed on the medial axis of the 3D target, which reduces optimization time and complexity.

What is claimed is:  
     
       1. A method for planning radiotherapy treatment comprising the steps of: 
       a) determining a first target region of a patient and locating a medial axis of a first target region of a patient;  
       b) initializing a plan for the distribution of a plurality of spherical distributions of radiation by identifying endpoints of the medial axis and determining a virtual shot for each endpoint of each plan;  
       c) providing additional virtual shots for each plan by excluding portions of said target region which are already covered by any virtual shot which has already been determined;  
       d) determining a medial axis for a modified target region which is established by excluding regions from said first target region which would be covered by any virtual shot which has already been determined;  
       e) placing additional virtual shots at endpoints or cross points of said medial axis for said modified target region to generate a distribution plan for targeting shots of radiation.  
     
     
       2. The method of claim  1  wherein steps c), d) and e) are repeated. 
     
     
       3. The method of claim  1  wherein steps c), d) and e) are repeated until a therapeutically acceptable portion of said first target region is covered by virtual shots. 
     
     
       4. The method of claim  3  wherein each virtual shot has a virtual size which is determined as dimensions of each said virtual shot where dose levels at a focal plain decrease from a predetermined percentage of a dose level which exists within said virtual shot. 
     
     
       5. The method of claim  3  wherein said dose level which exists within said virtual shot is assigned a value, and said predetermined percentage is less than 80%. 
     
     
       6. The method of claim  4  wherein said dose level which exists within said virtual shot is assigned a value, and said predetermined percentage is less than 65% and greater than 25%. 
     
     
       7. The method of claim  4  wherein said dose level which exists within said virtual shot is assigned a value, and said predetermined percentage is less than 65% and greater than 40%. 
     
     
       8. The method of claim  1  wherein said distribution plan is used to direct a radiation emitting device which can be used to provide a spherical distribution of radiation to position actual distributions of radiation according to said distribution plan. 
     
     
       9. The method of claim  8  wherein said radiation emitting device is selected from gamma emitting devices, linear accelerators, and Brachy therapy sources. 
     
     
       10. The method of claim  9  wherein said radiation emitting device is selected from the group consisting of gamma radiation emitting devices and linear accelerators. 
     
     
       11. The method of claim  8  wherein said distribution plans distributes radiation at a therapeutically effective dose level over at least 85% of said first target region. 
     
     
       12. The method of claim  11  wherein said therapeutically effective dose level is at least 40% of the highest single dose radiation level within any shot. 
     
     
       13. A method for planning and executing radiotherapy treatment comprising the steps of 
       (a) taking a non-invasive pictorial representation of a first target region of a volume portion of a patient which is to be treated by radiation therapy;  
       (b) locating a medial axis within the pictorial representation of the first target region of the patient;  
       (c) calculating from said pictorial representation a plan for the distribution of a plurality of spherical distributions of radiation by identifying endpoints of the medial axis and determining a virtual shot for each endpoint of each plan, said virtual shot at each endpoint having its assumed outer limits defined by a percentage of a therapeutically effective level of radiation which is provided in said virtual shot, the assumed outer limits of each virtual shot extending to at least two edges of the target region, said virtual shots at the endpoints virtually covering a part of the volume portion of the patient, and leaving a virtual untreated portion of said volume where minimally desired therapeutic levels of radiation have not yet been applied, the volume of said target area where minimally desired therapeutic levels of radiation have not yet been applied by virtual shots at the endpoints defining a modified target area;  
       (d) providing additional virtual shots for each plan within said virtual untreated portion of said volume by determining a modified medial axis for the modified target region which has been established;  
       (e) placing additional virtual shots at endpoints or cross points of said modified medial axis for said modified target region to generate a distribution plan for targeting shots of radiation comprising both the virtual shots at the endpoints of the medial axis and the virtual shots placed on said modified medial axis; and  
       (f) directing actual radiation treatment using said distribution plan for targeting shots of radiation.  
     
     
       14. The method of claim  13  performed by repeating steps c), d) and e), until a therapeutically acceptable portion of at least 60% of said first target region is covered by virtual shots. 
     
     
       15. The method of claim  13  wherein said distribution plan is used to direct a radiation emitting device which can be used to provide a spherical distribution of radiation to position actual distributions of radiation according to said distribution plan. 
     
     
       16. The method of claim  15  wherein said radiation emitting device is selected from gamma emitting device, linear accelerators, and Brachy therapy sources. 
     
     
       17. The method of claim  15  wherein said radiation emitting device is selected from the group consisting of gamma radiation emitting devices and linear accelerators. 
     
     
       18. The method of claim  15  wherein said distribution plans distributes radiation at a therapeutically effective dose level over at least 85% of said first target region. 
     
     
       19. The method of claim  18  wherein said therapeutically effective dose level is at least 40% of the highest single dose radiation level within any shot. 
     
     
       20. A system for planning and executing radiotherapy treatment comprising: 
       a) means for locating a medial axis of a first target region of a patient;  
       b) means for initializing a plan for the distribution of a plurality of spherical distributions of radiation by identifying endpoints of the medial axis and determining a virtual shot for each endpoint of each plan;  
       c) means for providing additional virtual shots for each plan by excluding portions of said target region which are already covered by any virtual shot which has already been determined;  
       d) means for determining a medial axis for a modified target region which is established by excluding regions from said first target region which would be covered by any virtual shot which has already been determined;  
       e) means for placing additional virtual shots at endpoints or cross points of said medial axis for said modified target region to generate a distribution plan for targeting shots of radiation; and  
       f) means for directing actual radiation treatment using said distribution plan for targeting shots of radiation.